This invention relates to methods for designing integrated circuits.
Integrated circuit design is a complex task involving many steps. The process typically begins with a circuit design that is specified in terms having little or nothing to do with how it can be implemented in an integrated circuit. This relatively abstract, starting circuit design passes through a succession of steps that gradually move it more and more toward a design specification for building an actual integrated circuit. As this process proceeds, it is very common for responsibility for it to pass from the people who have done the initial circuit design to different people who do the work that is closer to production of the integrated circuit. These may be two different groups of people in one company or organization, or they may be people in two different companies or organizations.
Various points in the above-described process have been used as the “signoff” point between the circuit design group and the integrated circuit (“IC”) design group. If the signoff point is relatively early in the process, the circuit design group's task is relatively easy, but it may be difficult or impossible for the IC design group to produce an IC design (and therefore an IC) that meets all the expectations and specifications of the circuit design group. For example, timing constraints supplied by the circuit design group may not be achievable by the IC design group, which may force the IC design group to return the project to the first group for a redesign. This is generally very undesirable for reasons such as cost, delay, and the like. On the other hand, the later in the process the signoff point is, the more difficult and time-consuming the circuit designers' part of the task is for them. Making the signoff point very late in the process takes the circuit designers into parts of the process that they may be less familiar with and/or less skilled at. It does, however, tend to increase the probability that what they hand off to the IC design group will be implementable without any circuit redesign and will have timing performance close to what is expected and desired.